1. FIELD OF THE INVENTION
The field of this invention lies within the magnetic tape art. More importantly, it lies within the streaming magnetic tape cartridge art, wherein information is continuously imparted to a tape by writing on the tape and in some cases, reading and validating the veracity of the information being written thereon. The art can be more finitely limited to the foregoing in cooperation with a multiple channel tape and an erasure system which erases the tape to provide for more accurate information in the form of digital information written thereon.
2. THE PRIOR ART
The prior art with respect to this invention lies within the streaming cartridge tape art, wherein information can be recorded at a density of eight thousand bits per inch. The tape drive incorporates a micro-computer which controls various drive functions and interfaces with a host system.
The streaming cartridge is particularly useful by virtue of the fact that in conventional tape systems, the recorded data is blocked and can be individually assessed and updated. To preserve the individuality of each record, the tape system must start and stop between records.
The foregoing requirement necessitates the incorporation of fairly long inter-record gaps. The length of the gaps is such that a conventional tape might only use approximately twenty eight percent of the magnetic media. This of course, is a substantial detriment, inasmuch as the recordation and utilization of the tape is quite inefficient. However, to record on a tape effectively and efficiently, substantial bits of information must be provided in juxtaposition to each other, in the respective bit cells. The closer the frequency of recording in each bit cell, the greater the inaccuracies occur for various reasons.
When the inaccuracies are limited, a streaming tape format can be approximately ninety seven percent efficient, due to the fact that the tape is not started and stopped over an extended period of time.
The streaming tape system provides maximum tape utilization at a high frequency rate for those applications that do not require tape systems that access and update individual records.
The streaming system can be utilized with certain time recording techniques wherein it first passes over a write and read head along a first or zero channel or track. The second track is obtained by reversing the tape direction and reading or writing with a second channel of the head, with the head body and tape in the initial relative position. On the return, the head, or in some cases the tape itself, can be moved to provide for a passage of the third or fourth tracks or channels in the same manner as the first and second channels.
The movement of the head body relative to the tape is a necessary requirement in order to record and read various tracks or channels of the tape. This invention eliminates the concepts and methods of the prior art in moving the head and incorporates a unique method for moving the head across the tape without degradation, oxide deterioration, and in the worst case, tearing or wrinkling of the tape.
The foregoing is accomplished by maintaining an air gap, an air cushion, or an air bearing over the surface of the head as it is moved across the tape. To do this, the head is moved laterally, while the tape is moving at the beginning or toward the end of the tape when no information is written or read thereon. In the alternative, when the tape is stopped at the end of the tape, the beginning of the tape, or possibly the middle of the tape, the capstan or drive is oscillated by pulsing the motor backwardly and forwardly to provide an air cushion between the tape and the head to prevent the lateral drag of the head as it moves across the tape.
An important feature of this invention resides within the fact that oftentimes information has to be recorded and erased on the tape. This can be either with regard to erasing at discrete times, or erasing the entire tape. Regardless of the foregoing, when the tape is erased, it must be erased so that a substantial amount of digital information can be recorded on the tape thereafter without any deleterious effect on the subsequently recorded information.
In the past, a DC type of erasure was utilized wherein the media was saturated at a particular point as it passed the field of the erase head. This drove all of the media into a particular magnetic mode, so that it retained substantial remanent magnetism in one direction. In this manner, the media was magnetized in one direction as a result of the DC erasure.
This invention utilizing AC erasure, provides an erase field that is alternated rapidly relative to the movement of the media across the erase head. The portion of the media erase gap is saturated alternately between two points. As the media is moved away from the erase head, it causes a slowly diminishing cyclic field and thereby diminishes the total magnetic induction down to a substantially small degree and sometimes to a substantial zero degree of magnetism within the tape. Thus, the media is left substantially unmagnetized, as the result of the AC erasure.
By having the tape in an unmagnetized condition, it allows the prospective magnetic writing to be uniform, and avoid asymmetries. This thereby provides for symmetrical digital peaks within the media when recordation takes place.
In the prior art, because of the fact that DC erasure is more pronounced, peak shift due to asymmetry of recording occurs because of the additive nature of the DC orientation of the tape.
Stated in another way, when a DC erasure has taken place, it results in an asymmetrical remanent induction on the tape. This in turn causes a resultant output voltage from the tape wherein the negative peaks are late and the positive peaks are early. In other words, the tape has been oriented in the positive direction upon erasure, so that in order for the negative recordation to take place, the magnetism on the tape must be driven downwardly through the previously established positive erasure or bias of the DC erasure. However, because of the fact that the positive peaks when recorded are additive, they are thereby caused to be early on the tape.
The late peaks correspond to flux reversals in a so called hard direction, in other words, a direction which is difficult to drive because of the DC orientation, which would be opposite to the direction of the DC erasure. On the other hand, the early peaks correspond to flux reversals in the easily driven direction or the same direction as the DC erasure. In effect, by its additive nature, it allows for easy movement in the originally erased direction and hard movement in the opposite direction from the original erasure.
When recording with AC erased media, the same delay of both negative and positive peaks occurs from the nominal in the read head output voltage wave form. In other words, inasmuch as the writing force does not have to drive against or be additive with regard to the orientation of the magnetism of the tape, a symmetrical recordation takes place. In effect, both the negative and positive digital information on the tape is symmetrical. This is usually formed in a manner whereby the negative and positive information is provided in symmetrically spaced late peaks.
The foregoing thereby provides for substantially greater recordation accuracy and closer orientation of the peaks within the particular center of a bit cell. Thus, AC erasures virtually eliminate the peak shifts caused by asymmetry in the recording process, and allows for more accurate information to be imparted on the tape. This thereby is a substantial step over the prior art in combination with the streaming tape cartridge drive system hereof.